Massive update. The highlights:
o dramatically cut memory usage by writing better, less intertwingled
code.
o implement booting off mmc/sd cards (sd only tested one at the moment)
o start to split out board specific stuff for boot2.
8k boundary with this program still.
text data bss dec hex filename
7925 4 4476 12405 3075 bootiic.out
so we have like 293 bytes left before we have to play games. There
may be ways to reduce that somewhat, but they start to be very board
specific.
changes in the future. This helps with getting started and to
overcome the really sucky level of granuality this timeout has in
getc. A timeout of 1 means 'wait until top of next second' rather
than 'wait for at least a second'.
Make this compile, assuming that you have linux installed in a
sensible place. tag_list is disabled by default, since we don't
distribute linux, but it is desirable to allow the boot loader to boot
Linux or FreeBSD (mostly for testing).
xmodem download. Then download the image you want in the flash.
This will burn the image into the flash. You must then reset the
unit and the new flash image will be used for booting...
xmodem download. Then download the image you want in the eeprom.
This will burn the image into the eeprom. You must then reset the
unit and the new eeprom image will be used for booting...
o Use a directory layout that is more akin to the i386 boot layout.
o Create a libat91 for library routines that are used by one or more
of the boot loaders.
o Create bootiic for booting from an iic part.
o Create bootspi for booting from an spi part.
o Optimize the size of many of these routines (especially emac.c). Except
for the emac.c optimizations, all these have been tested.
o eliminate the inc directory, libat91 superceeds it.
o Move linker.cfg up a layer to allow it to be shared.
For 32-bit SDRAM systems, enable D16 to D31 in the PIO controller.
Otherwise they read back as 0xffff.
Shave 8 bytes from the object size by using AT91C_BASE_PIOA directly
and by not assigning PIO_BSR to 0 in the DBGU init. That's a nop in
two ways (everything defaults to peripheral A, and writing 0 changes
nothing).
Many places used #define FOO ((unsigned int) 0x23) where a simpler
#define FOO 0x23u would have sufficed. This practice is overly
verbose and has the disadvantage that you can't say
#if FOO == BAR
#endif
because the extra "unsigned int" tokens choke cpp's little brain.
Migrate to the latter style to allow use in preprocessor statements.
The two are the same semantically anyway in a C context (at least for
the uses they are put to presently, C gurus can explain to me how they
differ).
via xmodem to the DBGU port when the AT91 comes up in recovery mode.
The recovery loader will then load your program via xmodem into SDRAM
at 1MB which can do its things. It needs to be tweaked to the
specific board one is using, but it fits in < 1kB (all of Atmel's ARM
products have at least 8kb of SRAM that I can tell, so this should
work for them all).
Parts of this code were provided by Kwikbyte with copyright
specifically disclaimed. I heavily modified it to act as a recovery
loader (before it was a bootstrap loader) and to optimize for size
(before I started the size was closer to 8k).
Bootstrap loaders for SPI and IIC to follow.
